Uptake Of 5-fluorouracil Research Articles

5-Fluorouracil uptake and release from pH-responsive nanogels: An experimental and computational study

Chemotherapy is the treatment of choice in cancer therapy even though anti-tumor agents cause frequent and harmful effects on organs and tissues. Nanogels can efficiently improve cancer therapy by increasing the antineoplastic concentration in tumor sites and acting on cancer cells for prolonged periods without significantly affecting normal tissues. In this research, a pH-responsive Polyvinylpyrrolidone (PVP)-based nanogel for the controlled release of 5-Fluorouracil (5-FU) was developed. Nanogels were synthesized using γ-radiation, and 5-FU was loaded into nanogels by physical entrapment. These formulations were characterized by spectroscopy techniques, electronic microscopy, and light scattering measurements. Drug loading and release from nanogels are strongly influenced by %PVP and irradiation dose. Simulations showed a higher drug-polymer affinity at low pH according to experimental loading values (encapsulation efficiency = 17% and drug loading = 83%). The sustained release profile responds to pH change from 1.2 to 7.4, increasing the release rate in acid conditions. Furthermore, nanogels have a negative surface charge, spherical morphology, and diameter of 41.0 ± 0.9 nm. These properties show its potential as a nanocarrier of 5-FU for cancer treatment.

Cytotoxicity and Cellular Uptake of 5-Fluorouracil Loaded Methylcellulose Nanohydrogel for Treatment of Oral Cancer

The objective of the study was to investigate the cytotoxicity and cellular uptake of prepared 5-Fluorouracil (5-FU) nano hydrogel formulation using KB oral cancer cell line and VERO fibroblast cell line. The biodegradable thermoresponsive modified methylcellulose (MMC) polymer was used for the preparation of nano hydrogel, whereas it shows a sol-gel phase transition at 36˚C to 40˚C. The physical crosslinking method was used, followed by probe sonication for the preparation of 5-FU loaded MMC nano hydrogel. The mechanism of crosslinking was studied by FT-IR and SEM. These experimental techniques explained physical crosslinking viz. H-bonding phenomenon with the interconnected porous structure of nanoscale pore size. Cytotoxicity assay in the concentration range from 1 µg/ml to 2000µg/ml shows an IC50 value at around 250µg/ml. This nano hydrogel shows concentration-dependent toxicity to the cancer cells while they were less toxic to normal fibroblast VERO cells. Cellular uptake was confirmed by the green fluorescence inside cells by Rhodamine-B conjugation using a fluorescent microscope. These results depict that 5-FU loaded thermosensitive nano hydrogel may be a promising candidate for intratumoral targeted drug delivery to cancer cells.

Fractional laser-assisted topical delivery leads to enhanced, accelerated and deeper cutaneous 5-fluorouracil uptake

ABSTRACTBackground: Topical 5-Fluorouracil (5-FU) exhibits suboptimal efficacy for non-melanoma skin cancer, attributed to insufficient intracutaneous penetration. This study investigates the impact of ablative fractional laser (AFXL) at different laser-channel depths on cutaneous 5-FU pharmacokinetics and biodistribution.Methods: In vitro porcine skin underwent AFXL-exposure using a fractional 10,600 nm CO2-laser, generating microscopic ablation zones (MAZ) reaching the dermoepidermal junction (MAZ-ED), superficial-(MAZ-DS), or mid-dermis(MAZ-DM). 5-FU in AFXL-exposed and control skin was measured in Franz diffusion cells at 4 and 24 hours (n = 55). HPLC quantified 5-FU in full-thickness skin, specific skin depths of 100μm-1500μm, and transcutaneous receiver-compartments. Qualitative matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) visualized 5-FU in selected samples.Results: Overall, AFXL enhanced and accelerated 5-FU uptake versus unexposed controls, with increased accumulation in deep skin layers (p < 0.01). While total, 24-hour 5-FU uptake in control skin was 0.096 mg/cm3 (0.19% of applied concentration), AFXL delivered up to 4.707 mg/cm3 (MAZ-DM; 9.41% uptake, 49-fold enhancement) (p = 0.002; 24 hours). Indicating accelerated delivery, 5-FU in laser-exposed samples at 4 hours was at least 10-fold that of 24-hour controls (p = 0.002). Deeper laser-channels increased delivery throughout the skin (MAZ-ED vs. MAZ-DM; p<0.01). MALDI-MSI confirmed enhanced, accelerated, deeper and more uniform 5-FU distribution after AFXL versus controls.Conclusions: AFXL offers laser-channel depth-dependent, enhanced and accelerated 5-FU uptake, with increased deposition in deep skin layers.

Transmembrane delivery of anticancer drugs through self-assembly of cyclic peptide nanotubes.

Breaking the natural barriers of cell membranes achieves fast entry of therapeutics, which leads to enhanced efficacy and helps overcome multiple drug resistance. Herein, transmembrane delivery of a series of small molecule anticancer drugs was achieved by the construction of artificial transmembrane nanochannels formed by self-assembly of cyclic peptide (cyclo[Gln-(d-Leu-Trp)4-d-Leu], CP) nanotubes (CPNTs) in the lipid bilayers. Our in vitro study in liposomes indicated that the transport of molecules with sizes smaller than 1.0 nm, which is the internal diameter of the CPNTs, could be significantly enhanced by CPNTs in a size-selective and dose-dependent manner. Facilitated uptake of 5-fluorouracil (5-FU) was also confirmed in the BEL7402 cell line. On the contrary, CPs could facilitate neither the transport across liposomal membranes nor the uptake by cell lines of cytarabine, a counterevidence drug with a size of 1.1 nm. CPs had a very weak anticancer efficacy, but could significantly reduce the IC50 of 5-FU in BEL7402, HeLa and S180 cell lines. Analysis by a q test revealed that a combination of 5-FU and CP had a synergistic effect in BEL7402 at all CP levels, in S180 at CP levels higher than 64 μg mL(-1), but not in HeLa, where an additive effect was observed. Temporarily, intratumoral injection is believed to be the best way for CP administration. In vivo imaging using (125)I radio-labelled CP confirmed that CPNPTs were completely localized in the tumor tissues, and translocation to other tissues was negligible. In vivo anticancer efficacy was studied in the grafted S180 solid tumor model in mice, and the results indicated that tumor growth was greatly inhibited by the combinatory use of 5-FU and CP, and a synergistic effect was observed at CP doses of 0.25 mg per kg bw. It is concluded that facilitated transmembrane delivery of anticancer drugs with sizes smaller than 1.0 nm was achieved, and the synergistic anticancer effect was confirmed both in cell lines and in vivo through the combinatory use of 5-FU and CP.

The influence of degradable starch microspheres on liver uptake of 5-fluorouracil after hepatic artery injection in the rat.

The effect of degradable starch microspheres (DSM) on the distribution of 5-fluorouracil (5-FU) after hepatic artery injection was studied in normal rats. Carbon-14-labelled 5-FU was injected separately or together with DSM into the hepatic artery. Radioactivity was measured in liver tissue, bile, peripheral blood, and urine. When microspheres were added, the liver uptake of 5-FU was increased; its peak concentration in peripheral blood decreased, as did the early urinary excretion of radioactivity. The addition of degradable starch microspheres to hepatic artery injections of cytostatic drugs might be of value in increasing the drug concentration in tumour tissue and reducing systemic toxicity.

Hyperoxia increases the uptake of 5-fluorouracil in mammary tumors independently of changes in interstitial fluid pressure and tumor stroma

BackgroundHypoxia is associated with increased resistance to chemo- and radiation-therapy. Hyperoxic treatment (hyperbaric oxygen) has previously been shown to potentiate the effect of some forms of chemotherapy, and this has been ascribed to enhanced cytotoxicity or neovascularisation. The aim of this study was to elucidate whether hyperoxia also enhances any actual uptake of 5FU (5-fluorouracil) into the tumor tissue and if this can be explained by changes in the interstitium and extracellular matrix.MethodsOne group of tumor bearing rats was exposed to repeated hyperbaric oxygen (HBO) treatment (2 bar, pO2 = 2 bar, 4 exposures à 90 min), whereas one group was exposed to one single identical HBO treatment. Animals housed under normal atmosphere (1 bar, pO2 = 0.2 bar) served as controls. Three doses of 5FU were tested for dose response. Uptake of [3H]-5FU in the tumor was assessed, with special reference to factors that might have contributed, such as interstitial fluid pressure (Pif), collagen content, oxygen stress (measured as malondialdehyd levels), lymphatics and transcapillary transport in the tumors.ResultsThe uptake of the cytostatic agent increases immediately after a single HBO treatment (more than 50%), but not 24 hours after the last repeated HBO treatment. Thus, the uptake is most likely related to the transient increase in oxygenation in the tumor tissue. Factors like tumor Pif and collagen content, which decreased significantly in the tumor interstitium after repeated HBO treatment, was without effect on the drug uptake.ConclusionWe showed that hyperoxia increases the uptake of [3H]-5FU in DMBA-induced mammary tumors per se, independently of changes in Pif, oxygen stress, collagen fibril density, or transendothelial transport alone. The mechanism by which such an uptake occur is still not elucidated, but it is clearly stimulated by elevated pO2.

Transferrin-conjugated liposomal system for improved delivery of 5-fluorouracil to brain

The objective of this study is to achieve the enhanced delivery of 5-fluorouracil to brain through transferrin-coupled liposomes. 5-Fluorouracil-loaded liposomes were prepared by cast film method and characterized for particle size, shape, percent encapsulation efficiency and in vitro drug release. Biodistribution studies were carried out with the help of radiolabelled 5-fluorouracil. 5-Fluorouracil was labelled with 99mTc-DTPA by oxidation–reduction method using stannous chloride and optimized for labelling parameters to get a high labelling efficiency. The in vitro stability was determined to check the efficiency of a system to find out the suitability of the radiolabelled system for in vivo studies. 99mTc-DTPA-labelled 5-fluorouracil bearing non-coupled and coupled liposomes were administered intravenously and biodistribution studies were performed. The distribution of 5-fluorouracil via non-coupled and coupled liposomes was determined in various organs, such as lungs, liver, kidneys, spleen and brain, by measuring the radioactivity using a gamma scintillation unit. The results of in vivo studies confirmed a selective uptake of the transferrin-coupled liposomes from the brain capillary endothelial cells. An average of 10-fold increase in the brain uptake of the drug was observed after the liposomal delivery of 5-fluorouracil, while the transferrin-coupled liposomes caused a 17-fold increase in the brain uptake of 5-fluorouracil.Therefore, it can be concluded that transferrin-coupled liposomes enhance the brain uptake of the drug, like 5-fluorouracil.

Carbogen Breathing Differentially Enhances Blood Plasma Volume and 5-Fluorouracil Uptake in Two Murine Colon Tumor Models with a Distinct Vascular Structure

For the systemic treatment of colorectal cancer, 5-fluorouracil (FU)-based chemotherapy is the standard. However, only a subset of patients responds to chemotherapy. Breathing of carbogen (95% O2 and 5% CO2) may increase the uptake of FU through changes in tumor physiology. This study aims to monitor in animal models in vivo the effects of carbogen breathing on tumor blood plasma volume, pH, and energy status, and on FU uptake and metabolism in two colon tumor models C38 and C26a, which differ in their vascular structure and hypoxic status. Phosphorus-31 magnetic resonance spectroscopy (MRS) was used to assess tumor pH and energy status, and fluorine-19 MRS was used to follow FU uptake and metabolism. Advanced magnetic resonance imaging methods using ultrasmall particles of iron oxide were performed to assess blood plasma volume. The results showed that carbogen breathing significantly decreased extracellular pH and increased tumor blood plasma volume and FU uptake in tumors. These effects were most significant in the C38 tumor line, which has the largest relative vascular area. In the C26a tumor line, carbogen breathing increased tumor growth delay by FU. In this study, carbogen breathing also enhanced systemic toxicity by FU.

Uptake of 5-fluorouracil (5-FU) in peritoneal metastases in relation to the route of drug administration and tumour debulking surgery: an autoradiographic study in the rat

Patients with peritoneal metastases from colorectal cancer have a poor prognosis. Aggressive treatment by debulking surgery and intraperitoneal (i.p.) chemotherapy has been suggested as an alternative therapy. However, the drug penetrance into the tumour in relation to the administration route and surgical reduction of the tumour is not well known. We compared locoregional administration with intravenous (i.v.) injection. Thirty-four in-bred rats with peritoneal metastases were randomly allocated into eight groups and injected with 14C-labelled 5-fluorouracil (5-FU) either through the i.v. or i.p. route, with or without a preceding tumour debulking, and were sacrificed after 2 or 8 h. Tumour radioactivity was visualised by autoradiography and quantified by a computer-based image analysis. After 8 h, 19 debulked and i.p.-injected tumours had a higher drug uptake, 63.2±28 (mean±standard deviation (SD)) kBq/g than 62 native i.p.-injected tumours (32.8±14) or 22 debulked and i.v.-injected tumours (18.5±18, P=0.002). After 8 h, 9 small tumours (<median 571 pixels) which underwent i.p. injection and tumour reduction had a higher drug uptake (77.4±26) than 29 non-debulked and i.p.-injected (35.1±17) or eight debulked and i.v. injected tumours (23.0±16, P=0.004). For larger tumours (⩾median 571 pixels), 16 debulked and i.p.-injected tumours had a higher radioactivity (drug uptake) (150.7±63) at 2 h than 49 i.p.-injected native tumours (48.5±59) or 11 reduced and i.v.-injected tumours (19.9±13, P=0.03). At 8 h, 10 debulked and i.p.-injected tumours had a higher drug uptake (50.3±24) than 33 native and i.p.-injected (30.8±10) or 14 debulked and i.v.-injected tumours (16.0±19, P=0.001). These results indicate that a debulking procedure and locoregional treatment of peritoneal metastases is associated with an increased level of 5-FU in the tumours.

Preoperative UFT administration for patients with advanced colorectal cancer - increased uptake of 5-fluorouracil by tumor tissue is a prognostic factor

The aim of this study was to clarify whether increased 5-fluorouracil (5-FU) uptake by tumor tissue following preoperative UFT administration is a prognostic factor after surgery in colorectal cancer patients. We examined the concentrations of 5-FU in tumor or normal tissue of 96 colorectal cancer patients who received UFT (400 mg/day) orally for 7 days prior to surgery. Patients were divided into two groups with high or low 5-FU concentrations in tumor tissue (defined as higher or lower than the cut-off value, respectively). The cut-off value of 5-FU was established based on the upper limit of the 95% confidence interval of the median of the concentration found in normal tissue (0.106 microg/g). Of the 96 patients, 62 (64.6%) were in the low-5-FU group and 34 (35.4%) in the high-5-FU group. The latter had a more favorable clinical outcome (p=0.0465). Cox regression analysis revealed that two independent variables, stage and 5-FU status in tumor tissue, were significant for prediction of survival. These findings suggest that increased uptake of 5-FU by tumor tissue following preoperative oral administration of UFT is an independent prognostic factor in colorectal cancer patients. This variable needs to be considered in the design of future therapeutic trials.

Vasopressin Selectively Increases 5-Fluorouracil Uptake by Colorectal Liver Metastases Following Hepatic Artery Bolus Infusion

Background.Poor drug uptake secondary to the hypovascularity of colorectal liver metastases may partially explain their limited response to hepatic artery chemotherapy. Vasoconstrictors can increase tumor perfusion but their effect on drug uptake has not been well-characterized. The aim of this study was to determine whether vasopressin could selectively increase tumor uptake of 5-FU.Materials and methods.A syngeneic rat model of colorectal liver metastases was used. Control group rats underwent a 60-s hepatic artery infusion of14C-5-FU (30 mCi/150 μL). Treatment group rats had vasopressin (60 mIU/kg, dose determined in pilot study) added to the14C-5-FU infusion. Mean systemic arterial pressure was minimally affected. Tumor:liver (T/L UR) and tumor center:periphery (C/P UR) 5-FU uptake ratios were determined using quantitative autoradiography techniques. Differences in tumor size (< or > 4 mm) and location (superficial vs deep) were accounted for. Statistical analysis was by repeated measures ANOVA (P= 0.01 significant).Results.A total of 161 tumors in 18 rats was analyzed. T/L URs were significantly higher in the treatment group compared to controls for tumors <4 mm (1.72 ± 0.14 vs 0.70 ± 0.16,P<0.001), tumors >4 mm (0.99 ± 0.15 vs 0.45 ± 0.16,P= 0.01), deep tumors (1.17 ± 0.13 vs 0.68 ± 0.15,P= 0.01), and superficial tumors (1.54 ± 0.15 vs 0.47 ± 0.17,P<0.001). C/P URs did not differ significantly between the groups.Conclusions.The results of this study show that vasopressin selectively enhances the uptake of 5-FU by colorectal liver metastases in a rat model of hepatic artery infusion. This may represent a promising strategy for improving tumor response rates and patient survival.

Influence of pH on the uptake of 5-fluorouracil into isolated tumour cells.

To investigate the possible dependence of 5-fluorouracil (5FU) uptake in tumours on the intra- (pHi) and extracellular (pHe) pH, a pH gradient (deltapH) was imposed across the plasma membrane of ascites tumour cells in vitro, similar to that known to occur in some solid tumours in vivo, by incubation in media of PHe 5-8. A > or = 2:1 (intracellular/extracellular) accumulation of radiolabelled 5FU occurred after 5 min incubation of the cells with 0.5 mM 5FU at pHe of 5.0, 5.5 or 6.0. 5FU metabolism is slow under these conditions, and 5FU uptake was not affected by longer incubations up to 20 min, nor by the absence of a sodium gradient. pHi was estimated from the distribution of the weak acid, 5.5-dimethyl-2,4-oxazolidione ([14C]DMO) across the cell membrane. There was significant correlation between the intracellular/extracellular 5FU ratio and pHe (from pHe 6-8), deltapH and pHi (P < 0.02). Similar results were obtained with HT29 cells. Incubation with a drug that made plasma membranes permeable to H+ significantly decreased 5FU uptake in Lettre cells. The co-transport of 5FU may occur on a proton symport using the proton motive force of the deltapH.

Potent induction of human colon cancer cell uptake of chemotherapeutic drugs by N-myristoylated protein kinase C-alpha (PKC-alpha) pseudosubstrate peptides through a P-glycoprotein-independent mechanism.

Phorbol ester protein kinase C (PKC) activators and PKC isozyme over-expression have been shown to significantly reduce intracellular accumulation of chemotherapeutic drugs, in association with the induction of multidrug resistance (MDR) in drug-sensitive cancer cells and enhancement of drug resistance in MDR cancer cells. These observations constitute solid evidence that PKC plays a significant role in the MDR phenotype of cancer cells. PKC-catalyzed phosphorylation of the drug-efflux pump P-glycoprotein was recently ruled out as a contributing factor in MDR. At present, the sole drug transport-related event that has been identified as a component of the role of PKC in MDR is PKC-induced expression of the P-glycoprotein-encoding gene mdr1. The objective of this study was to test the hypothesis that PKC can modulate the uptake of chemotherapeutic drugs in cancer cells independently of P-glycoprotein. We analyzed the effects of selective PKC activators/inhibitors on the uptake of radiolabelled cytotoxic drugs by cultured human colon cancer cells that lacked P-glycoprotein activity and did not express the drug efflux pump at the level of message (mdr1) or protein. We found that the selective PKC activator 12-O-tetradecanoylphorbol-13-acetate (TPA) significantly reduced uptake of [14C] Adriamycin and [3H] vincristine in human colon cancer cells devoid of P-glycoprotein activity, and that PKC-inhibitory N-myristoylated PKC-alpha pseudosubstrate synthetic peptides potently and selectively induced uptake of the cytotoxic drugs in the phorbol ester-treated and non-treated colon cancer cells. TPA treatment of the cells did not induce expression of either P-glycoprotein or its message mdr1. In contrast with [14C]Adriamycin and [3H] vincristine uptake, [3H] 5-fluorouracil uptake by the cells was unaffected by TPA and reduced by the PKC-inhibitory peptides. These results indicate that PKC activation can significantly reduce the uptake of multiple cytotoxic drugs by cancer cells independently of P-glycoprotein, and that N-myristoylated PKC-alpha pseudosubstrate peptides potently and selectively induce uptake of multiple cytotoxic drugs in cultured human colon cancer cells by a novel mechanism that does not involve P-glycoprotein and may involve PKC isozyme inhibition. Thus, N-myristoylated PKC-alpha pseudosubstrate peptides may offer a basis for the development of agents that reverse intrinsic drug resistance in human colon cancer.

19 F Nuclear Magnetic Resonance Analysis of 5-Fluorouracil Metabolism in Four Differently Pigmented Strains of Nectria haematococca

F nuclear magnetic resonance spectroscopy was used to study the metabolism of 5-fluorouracil in four strains of Nectria haematococca which displayed similar sensitivities to growth inhibition by this compound but differed in their pigmentation. The major metabolites, 5-fluorouridine and alpha-fluoro-beta-alanine, were excreted into the medium by all four strains. The classical ribofluoronucleotides (5-fluorouridine-5'-monophosphate, -diphosphate, and -triphosphate) and alpha-fluoro-beta-alanine were identified in the acid-soluble fraction of perchloric acid extracts of mycelia. Two hydrolysis products of 5-fluorouracil incorporated into RNA were found in the acid-insoluble pool. They were unambiguously assigned to 5-fluorouridine-2'-monophosphate and 3'-monophosphate with specific hydrolysis reactions on isolated RNA. The lack of fluorodeoxyribonucleotides and the fact that the four strains incorporated similar amounts of fluororibonucleotides into their RNAs strongly suggest an RNA-directed mechanism of cytotoxicity for 5-fluorouracil. The heavily pigmented wild type differed from the three low-pigmented strains in its low uptake of 5-fluorouracil and, consequently, in its reduced biosynthesis of 5-fluorouridine and alpha-fluoro-beta-alanine. At present, it is not clear whether this change in 5-fluorouracil metabolism is a side effect of pigment production or results from another event.

Absorption and lymphatic uptake of 5-fluorouracil in the rat following oral administration of w/o/w multiple emulsions

The influence of the nature of the oil phase of w/o/w emulsions on the oral absorption of 5-fluoro[ 3H]uracil in the rat is described. Liver levels and lymphatic accumulation of the drug following oral administration of w/o/w emulsions were studied. The absorption of 5-fluoro[ 3H]uracil orally administered in a water/isopropyl myristate/water emulsion was enhanced compared to an aqueous solution while a w/o/w emulsion prepared with octane as the oil phase reduced intestinal uptake. The suggested mechanism underlying the enhancement noted with isopropyl myristate emulsions may be attributed to the inhibitory effect of the oil on the gastric emptying processes. Both emulsion systems showed potential as lymphotropic carriers of water-soluble drugs to the mesenteric lymph nodes following oral administration.

Mechanisms of potentiation of antitumor activity of 5-fluorouracil by ribothymidine in a mouse tumor system.

In the presence of ribothymidine, the uptake of 5-fluorouracil (5-FU) was enhanced in Ehrlich ascites carcinoma cells in vitro, and was efficiently converted to FU-nucleotides. In these cells, almost all ribothymidine was found to be converted to thymine by, presumably, uridine phosphorylase. The enhanced uptake of 5-FU and its efficient conversion to FU-nucleotides were also observed in Ehrlich ascites carcinoma of ribothymidine-coadministered mice. The radioactivity of 5-FU-14C in the carcinoma cells, which was detected mainly in the acid-soluble fraction immediately after the administration and then shifted to the ribonucleic acid fraction, was approximately 2-fold higher in the ribothymidine-coadministered group than in the control group. On the other hand, ribothymidine-14C was also taken up by the carcinoma cells and an appreciable portion of its radioactivity appeared in the thymine fraction. Thymine produced from ribothymidine-14C was also detected in the extracellular ascitic fluid. The conversion of ribothymidine to thymine was assumed to be catalyzed by uridine phosphorylase, suggesting that ribose 1-phosphate was coproduced and served as a ribose donor for 5-FU. These results suggest that ribothymidine may act as a ribose donor for 5-FU to form FU-nucleotides via 5-fluorouridine in carcinoma cells, resulting in the potentiation of 5-FU activity.

Enhancement of 5-fluorouracil uptake into the bacterial cell by piperacillin.

The antibacterial activity of 5-fluorouracil, an antineoplastic agent, was found to be enhanced by piperacillin, a beta-lactam antibiotic, resulting in a synergism. It was considered that the synergism was caused by an increase of 5-fluorouracil uptake into the bacterial cell. On the other hand, amount of piperacillin bound to penicillin binding protein (PBP) did not change when 5-fluorouracil was added. The morphological change of the cell was due to the 5-fluorouracil when synergism appeared between 5-fluorouracil and piperacillin.

The mode of uptake of 5-fluorouracil(5-FU) by dimethyl-hydrazine (DMH) induced rat colo-rectal tumour tissues : L.S.F. Hsu and D. Burston. Department of Experimental Pathology, Westminster Medical School, London SW1, U.K.

The mode of uptake of 5-fluorouracil(5-FU) by dimethyl-hydrazine (DMH) induced rat colo-rectal tumour tissues : L.S.F. Hsu and D. Burston. Department of Experimental Pathology, Westminster Medical School, London SW1, U.K.

Enhancement and depression by inosine of the growth inhibitory action of 5-fluorouracil on cultured Jensen tumor cells

Continuous exposure of Jensen tumor cells in vitro to 1 mM inosine following a 1 hr exposure to 5-fluorouracil resulted in a 5-fold potentiation of growth inhibition. This effect was abolished by the simultaneous presence of 1 mM cytidine and was attributable to altered metabolic processing of drug anabolites after the uptake of 5-fluorouracil had ceased. In contrast, antagonism to 5-fluorouracil was seen when the cells were exposed successively to 1 mM inosine for 1.5 hr and to 5-fluorouracil for 1 hr. In this case the inhibitory action of the drug was diminished by nearly one-half. Quantitation of the potentiation and antagonism was based upon growth delays measured from growth curves obtained by serial photomicrography.

The kinetics of uptake of 5-fluorouracil by rat liver.

1 Slices of rat liver weighing 15-30 mg were incubated at 37 degrees C in 5-fluorourecil (5-FU) solution. 2 The 5-FU taken up was measured by high pressure liquid chromatography. 3 Uptake of 5-FU was found to approximate to Michaelis-Menton kinetics with the values of Kt and Vmax equal to 15.39 mmol 1-1 and 1.96 mumol g-1 min-1 respectively. 4 Transport of 5-FU was saturable with the uptake being much greater in the non-fasting rats. 5 Intracellular concentration of 5-FU after 24 min incubation approached but did not significantly exceed that in the extracellular fluid. 6 Enzymatic destruction of 5-FU at 2 min was negligible but substantial after a long incubation period. 7 2,4-Dinitrophenol was found to inhibit transport of 5-FU significantly. 8 Results suggested that the mechanism of uptake of 5-FU by rat liver is an energy requiring process.